The present invention relates to an engine braking device for a combustion engine in motor vehicles, in particular in commercial vehicles. The invention furthermore relates to a method and to a vehicle having the engine braking device.
In air-compressing (diesel) combustion engines in commercial vehicles, there is a known practice of producing an exhaust gas backpressure in the exhaust system by a brake flap in the overrun mode, the backpressure bringing about effective engine braking since the pistons of the combustion engine operate against this exhaust gas pressure during the exhaust stroke (outlet valves open).
In order to significantly increase the effect of such an engine braking device, there is a widely known practice of additionally providing a decompression brake, where, in addition to regular valve actuation in accordance with the four-stroke principle, the outlet valves are also partially open during the compression stroke. Here, the additional braking effect arises from the throttled discharge of the combustion air into the exhaust system.
The decompression brake can be either exhaust-controlled or positively controlled. In exhaust-controlled operation, the valve timing of the outlet valves is configured in such a way that the outlet valves open irregularly in a specifically intended manner owing to the exhaust gas backpressure present when the brake flap is closed (“valve jumping”) and are held open by a mechanism until the next regular valve opening.
In the case of a positively controlled decompression brake, interventions are generally made into the regular valve timing by hydraulic and mechanical means in order to hold the outlet valves partially open in a specifically intended manner, at least also during the compression stroke.
For example, AT 512 332 A1 discloses a throttling device integrated into the exhaust turbine for the open-loop and/or closed-loop control of an engine braking mode, in which a brake flap in the housing of the exhaust turbine is inserted into the rotor mounting space accommodating a turbine rotor directly in the region of the mouth of an inflow duct of the exhaust turbine. A measure of this kind requires design modifications to the turbine structure and is therefore relatively expensive.